Which condition must be met before an environment can support CSC?

Question

Options

• AThe CSC-PE and CSC-CE must each be able to ping an interface in its respective global routing
• BThe CSC-PE and the CSC-CE must support IPv6.
• CThe CSC-PE and CSC-CE devices must be able to send labels to one another using BGP.
• DThe CSC-CE must support OSPFv3.

• A
  8% (4)
• B
  16% (8)
• C
  71% (35)
• D
  4% (2)

Explanation

Option C is correct because CSC (Carrier Supporting Carrier) is fundamentally an MPLS architecture where a customer carrier's traffic must maintain label-switched paths across a backbone carrier's network. For this to work, the CSC-PE (backbone carrier's edge router) and CSC-CE (customer carrier's edge router) must exchange MPLS labels via BGP (specifically BGP Labeled Unicast / BGP-LU) - without this label exchange, the customer carrier cannot extend its own MPLS forwarding across the backbone.

Why the distractors are wrong:

• A - Basic ping reachability is a general networking prerequisite, not a CSC-specific requirement, and does not enable label distribution.
• B - CSC is an MPLS/IPv4 architecture; IPv6 support is not required and is unrelated to the CSC design.
• D - OSPFv3 is the IPv6 variant of OSPF and has no mandatory role in CSC; the PE-CE routing protocol can be BGP, OSPF (v2), or others.

Memory tip: Think of CSC as "Carriers Sharing (BGP) Labels." The entire point of CSC is that the backbone carrier's network becomes transparent to the customer carrier's MPLS, and that transparency only works if labels are passed between the two edge routers via BGP - everything else is secondary.

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